In some parts of the world, geothermal reservoirs are being used in the generation of energy. Typically, the geothermal reservoirs are tapped by drilling a well or several wells into the reservoir. High temperatures in the reservoir generate hot geothermal steam from naturally occurring water in the reservoir. The geothermal steam is gathered from the well or wells and transported through pipelines to a generating station, such as a steam turbine-driven electrical generator. In addition to relatively condensable water vapor, the geothermal steam typically includes relatively non-condensable gases, such as carbon dioxide, methane, nitrogen, hydrogen sulfide and hydrogen.
In the generation of power from geothermal steam using steam turbines, the proportion of non-condensable gases in the geothermal steam affects the efficiency of conversion of the energy in the geothermal steam to drive the turbine. The steam turbines operate by receiving the geothermal steam and drawing the geothermal steam through the turbine blades to cause the turbine to turn. Geothermal steam is drawn through the turbine blades typically by placing a condenser downstream from the turbine. The condenser condenses the condensable gases from the geothermal steam and creates a partial vacuum that serves to draw the geothermal steam through the turbine blades. However, the non-condensable gases in the geothermal steam tend to defeat the vacuum created by the condenser and thereby decrease the efficiency of the turbine. Therefore, it is desirable to measure the proportion of non-condensable gases in the geothermal steam so that performance criteria can be analyzed and for other reasons.
One prior art method for measuring the proportion of non-condensable gases in geothermal steam is described by Dr. Donald E. Michels ("CO.sub.2 and Geothermal Steam: A Rapid, Precise, and Accurate Field Assay Technique", Transactions, Geothermal Resources Council, Vol. 2, July 1978, pp. 445-448). In the Michels method, the goethermal steam line pressure drives a sample into a syringe that holds it at a known volume during equilibration. The syringe collects the non-condensable gases and equilibrates them with the condensate of the condensable gases at ice water temperature. The Michels method involves a closed system in which the geothermal steam is supplied to a known volume at a known temperature and driven by the absolute pressure of the steam line. The volume of condensate and uncondensed gases can be observed in the syringe and the proportion of non-condensable gases in the steam line can be calculated from those observed parameters.
The Michels method is only capable of supplying a maximum of six to eight determinations per hour. Thus, it is a relatively non-continuous measurement.
Another prior art closed system for measuring the proportion of non-condensable gases in a flow of geothermal steam is described by G. D. McDowell ("An Instrument for Measuring the Gas Concentrations in Geothermal Wells", GEOTHERMICS (1974) Vol. 3, No. 3, pp. 110-104). The instrument described by McDowell directly measures the partial pressure of the non-condensable gases present in a closed sample of the total mixture of geothermal steam, at a given temperature and given total pressure. This measurement is achieved by deducting the vapor pressure of distilled water at the given temperature derived from standard tables from the combined pressure of the water vapor and non-condensable gases present in the closed sample. However, this method is apparently only accurate when the non-condensable gas content of the geothermal steam is high and the steam line pressure completely stable.